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Potassium-40

Properties and data of the isotope 40K.

 

See also: list of Potassium isotopes.

 

General data

Name of the isotope:Potassium-40; K-40Symbol:40KMass number A:40Atomic number Z:19 (= number of protons)Neutrons N:21Isotopic mass:39.9639982(4) u (atomic weight of Potassium-40)Nuclide mass:39.9535754 u (calculated nuclear mass without electrons)Mass excess:-33.53546 MeVMass defect:0.366640644 u (per nucleus)Nuclear binding energy:341.52356004 MeV (per nucleus)
8.538089 MeV (average binding energy per nucleon)
Separation energy:SN = 7.79962(6) MeV (first neutron)
SP = 7.582(5) MeV (first proton)
Half-life:1.248(3) × 109 aDecay constant λ:1.761182124173 × 10-17 s-1Spin and parity:4-Charge radius:3.4381(28) femtometer fmYear of discovery:1935

 

Radioactive Decay

Half-life T½ = 1.248(3) × 109 a respectively 3.9356928 × 1016 seconds s.

Decay modeDaughterProbabilityDecay energyγ energy
(intensity)
β-40Ca89,28(11) %1,31089(6) MeV
EE/β+40Ar10,72(11) %1,50440(6) MeV1,460820(5) MeV
10,66(17) %

 

Occurrence

Comparison of the natural Kalium isotopes including isotopic abundance (proportion of the isotope mixture):

 

Atomic Mass maQuantityHalf-lifeSpin
Kalium
Isotopic mixture
39,0983 u100 %
Isotope 39K38,96370649(3) u93,2581(44) %stable3/2+
Isotope 40K39,9639982(4) u0,0117(1) %1.248(3) × 109 a4-
Isotope 41K40,96182526(3) u6,7302(44) %stable3/2+

 

NMR data

40K belongs to the NMR active Nuclides.

Isotope:40K-NMRQuantity:0,0117(1) %Spin:4-Nuclearmagnetic moment
μ/μN:
-1,29797(3)Quadrupole moment
Q fm-2:
-7,50(8)Resonance frequency
v0 at 1 T:
2,4737Relative Sensitivity:0,00523 (H0 = const.)
1,5493 (v0 = const.)
[related to 1H = 1,000]

 

Radiation Protection

Kaliumverbindungen und -präparate sind in Natur, Technik und Alltag allgegenwärtig vorhanden und gelten trotz des Anteils an K-40 nicht als radioaktive Gefahrstoffe; dazu ist die davon ausgehende Strahlung zu schwach.

Mit 40K angereicherte Substanzen haben praktisch und technisch keinerlei Bedeutung; K-40 zählt zu den radioaktiven Substanzen, bei denen auch hohe Aktivitäten nicht zu einer Einstufung als hochradioaktive Strahlenquelle führen.

The German Radiation Protection Ordinance, for example, specifies the following limit values for the isotope Potassium-40 (exemption limits, clearance values and other values as a radioactive or highly radioactive source of radiation (HASS)):

Isotope:K-40Exemption level:106 BqExemption level per gram:100 Bq/g
Unrestricted handling of solids and liquids.
Activity HASS:Unbegrenzt (UL)Surface contamination:10 Bq/cm2Half-life:1.3 × 109 a

 

Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear IsomerExcitation EnergyHalf-lifeSpin
40mK1643,638(11) keV0,336(13) μs0+

 

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 21) and isobaric (same nucleon number A = 40) with Potassium-40. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

 

OZIsotone N = 21Isobar A = 40
930F
1031Ne
1132Na
1233Mg40Mg
1334Al40Al
1435Si40Si
1536P40P
1637S40S
1738Cl40Cl
1839Ar40Ar
1940K40K
2041Ca40Ca
2142Sc40Sc
2243Ti40Ti
2344V40V
2445Cr
2546Mn
2647Fe
2748Co
2849Ni

 

External data and identifiers

CAS:13966-00-2InChI Key:ZLMJMSJWJFRBEC-OUBTZVSYSA-NInChI Code:[40K]PubChem:ID 6328542Adopted Levels, Gammas:NuDat 40K

 

Literature and References

[1] - H. Leutz, G. Schulz, H. Wenninger:
The decay of potassium-40.
In: Zeitschrift für Physik, (1965), DOI 10.1007/BF01387190.

[2] - A. Ažman, A. Moljk, J. Pahor:
Electron capture in potassium 40.
In: Zeitschrift für Physik A, (1968), DOI 10.1007/BF01379914.

[3] - W. Sahm, A. Schwenk:
39K, 40K and 41K Nuclear Magnetic Resonance Studies.
In: Zeitschrift für Naturforschung A, (2014), DOI 10.1515/zna-1974-1208.

 


Category: Isotopes

Last update: 24.10.2020



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